The present invention relates to an industrial data transmission system for the registering of process parameters in a periodic bus cycle with a fixed time frame, a synchronizing signal within each cycle having the effect in each case that a multiplicity of process parameters are simultaneously registered and recorded and, in a subsequent data exchange phase, are transmitted to an open-loop and/or closed-loop process control system.
It is known from the printed document xe2x80x9cStandardisierter Feldbus fur die elektrische Antriebstechnikxe2x80x9d [standardized field bus for electrical drive engineering], VDI reports, 844, xe2x80x9cSERCOS interfacexe2x80x9d report, page 69 ff., that a time-controlled bus access to drives can be performed with the aid of the SERCOS interface. The data messages which are intended for the individual drives are sent in a fixed time frame. An open-loop or closed-loop control system undertakes the master function and, at the cycle time intervals, sends a synchronizing signal, in response to which the individual drives, known as the slaves, transmit their information to the master.
In the open-loop and closed-loop control of production machines, in particular plastics injection-molding and/or blow-molding installations, precise measured data acquisition and high control accuracy of the final control elements is of great importance for ensuring the quality of the parts produced. A prerequisite for rapid and precise closed-loop control is the smallest possible time span between the reception of the actual process values of the sensor and the processing, and also the subsequent output of new setpoint values to an actuator.
Nowadays, a large number of products or intermediates which are used in industry and in the consumer goods sector are produced by plastics injection-molding and/or blow-molding installations. These products have to meet increasingly high requirements in terms of production quality. The object of the invention is to provide an industrial data transmission system with process requirements optimized for plastics injection-molding and/or blow-molding installations.
According to the present invention, the object is achieved by having all of the time-critical process input and output parameters registered simultaneously for the open-loop and closed-loop control of a plastics injection-molding and/or blowmolding installation. The process peripherals, which in such installations may for example be arranged decentrally from the open-loop or closed-loop control system, record all the measured parameters with the synchronizing signal. The measured data are consequently not acquired asynchronously in relation to one another and can advantageously be processed in the open-loop and closed-loop control system with a fixed time reference point.
A first preferred design of the present invention is characterized in that, after the data exchange phase with decentralized process peripherals, there follows an openloop and/or closed-loop process control phase for high-priority process parameters. The time interval from the measured data acquisition (synchronizing signal) until the processing (open-loop and/or closed-loop control phase) is at the least within the time segment for the processing of high-priority process parameters. In the open-loop and/or closed-loop process control phase for high-priority process parameters, predominantly only time-critical process variables are processed. This procedure ensures that an immediate response can be made in particular to time-critical process changes.
A further preferred design of the present invention is characterized in that, after the data exchange phase, there occurs a high-priority detection of the changeover point for plastics injection-molding machines, at which time a change is made from an injection operation to a holding-pressure operation. During the operation of injecting the plastic, the injection pressure constitutes a time-critical process parameter.
To achieve the highest possible number of units in the production process, a high rate of injection into the injection mold is used. When the injection mold is filled, undiminished maintenance of the rate of injection leads to a high increase in pressure. The open-loop and/or closed-loop process control system must consequently register the changeover point, at which time a significant increase in pressure occurs at a rapid rate, as quickly as possible and respond to it as quickly as possible. This is ensured in the present invention by the data exchange phase being directly followed by a computing operation time for detection of the changeover point, which initiates further closed-loop or open-loop control steps immediately when detection occurs.
A further preferred design of the present invention is characterized in that a periodically recurring machine production cycle comprises bus subeycles, which are respectively provided with a synchronizing signal and have different information contents and/or different lengths. Different measured process variables generally also have different process time constants. To allow for these properties in an advantageous way, the production cycle of an injection-molded part can be broken down into a specific number of bus subcycles. It is not always necessary to measure all the process variables in these subcycles. In particular in the case of measured parameters with large time constants in comparison with the system, it may for example, be advisable to register these in every second bus subcycle or at even greater time intervals. The different lengths and different information contents of the bus subcycles have the effect that time-critical measured parameters can on average be measured at shorter time intervals, in comparison with a measuring system which registers all the measured parameters in every cycle. Consequently, the response time to a time-critical event is also advantageously diminished.